1. Field of the Invention
In this specification, a technique relating to a method for manufacturing a substrate having a silicon-on-insulator (SOI) structure in which a semiconductor layer is provided on a substrate with an insulating layer interposed therebetween is described. Further, a technique relating to a reprocessing method of a semiconductor wafer which has been used in manufacturing this SOI substrate is described.
2. Description of the Related Art
A semiconductor substrate having an SOI structure (hereinafter referred to as an SOI substrate) in which a semiconductor layer is provided on a substrate with an insulating layer interposed therebetween has attracted attention as a substrate suitable for manufacturing an LSI which has low power consumption and can operate at high speed.
One of known methods for manufacturing an SOI substrate is a hydrogen ion implantation separation method (e.g., see Patent Document 1). As described in Patent Document 1, an SOI substrate is manufactured using two bulk silicon wafers in the hydrogen ion implantation separation method. One of the two bulk silicon wafers serves as a bond substrate (also referred to as a donor substrate) and the other serves as a base substrate. The bond substrate provides a semiconductor layer, and the base substrate forms the SOI substrate body. A method for manufacturing an SOI substrate by the hydrogen ion implantation separation method is briefly described below.
An oxide film is formed on the bond substrate by a thermal oxidation method, and then irradiation with hydrogen ions is performed to form a microbubble layer inside the bond substrate. Then, the bond substrate and the base substrate are disposed in close contact with each other with the oxide film interposed therebetween and bonded to each other. After that, heat treatment is performed and the bond substrate is divided at the microbubble layer, so that a silicon layer is formed on the base substrate with a thermal oxide film (insulating layer) interposed therebetween. The silicon layer is a semiconductor layer which has been separated from the bond substrate. Then, heat treatment or the like is performed on the base substrate in order to strengthen the attachment between the silicon layer and the base substrate, so that an SOI substrate is completed. Further, in the hydrogen ion implantation separation method, the bond substrate from which the silicon layer has been separated can be reused, and the used bond substrate is reprocessed and reused.
However, oxygen is incorporated into the bond substrate because of the manufacturing method; therefore, crystal defects due to oxygen such as oxide precipitate, dislocation, or stacking fault are formed in the vicinity of a surface of the bond substrate which forms the semiconductor layer by heat treatment in the manufacturing process of an SOI substrate (typically, heat treatment in a step of forming the thermal oxide film and a step of dividing the bond substrate). Accordingly, the crystal defects in the vicinity of the surface need to be reduced in order to reuse the bond substrate.
For example, Non-Patent Document 1 discloses that crystal defects in the vicinity of a surface of a CZ silicon wafer can be reduced by annealing at 1200° C. under a hydrogen gas atmosphere (the proportion of the hydrogen is 100%).
In addition, Patent Documents 2 to 4 each disclose reuse of a bond substrate.
Patent Document 2 discloses that in order to increase the number of times of use of a bond substrate, a silicon wafer formed by slicing an ingot is used for a bond substrate. The ingot is grown by a CZ method and includes neither aggregate of vacancy-type point defects whose oxygen concentration is 5×1017 atoms/cm3 to 14×1017 atoms/cm3, nor aggregate of interstitial-silicon-type point defects.
Patent Document 3 discloses that by performing heat treatment rapidly on a bond substrate from which a silicon layer has been separated at 1150° C. to 1300° C., oxide precipitate in the bond substrate can be reduced.
Patent Document 4 discloses that a CZ wafer with few defects whose whole surface is formed using an N region is used as a bond substrate and RTA treatment is performed as reprocessing treatment of the bond substrate at higher temperature than that in a step of forming a thermal oxide film performed on the bond substrate.